How to use Bio-Logic products to test batteries ?

N. Murer

Outline

1. Configuration

2. DC techniques

3. Impedance spectroscopy

4. Processing data

• REF1 : Red – for the control and the measurement of the working electrode potential.

• REF2 : White – for the control and the measurement of the reference electrode potential.

• REF3 : Blue – for the control and the measurement of the counter electrode potential.

• CA2 (Control amplifier): Red – for the control and the measurement of the working electrode current (standard mode).

• CA1: Blue – for the control and the measurement of the counter electrode current (standard mode).

• GND (Ground): Black

Configuration

Two points connection + WE = CA2 + REF1 - CE = CA1 + REF2 + REF3

Configuration

+

-

CA2 + REF1

CA1 + REF2 + REF3

TO BE AVOIDED

Three points connection + WE = CA2 (for current) REF1 (for potential) - CE = CA1 (for current)

REF3 (for potential)

+

-

CA2

CA1

Four points connection + WE = CA2 (for current) REF1 (for potential) - CE = CA1 (for current)

REF2 + REF3 (for potential)

+

-

CA2

CA1

REF1

REF2 + REF3

OK

REF1

REF3

OK REF2

REF = REF2

Additional recording conditions

Parameters for the intercalation coefficient

Cell description

Reference electrode

Cell connection mode

Cell Characteristics

Batteries Testing Applications

Outline

1. Configuration

2. DC techniques

3. Impedance spectroscopy

4. Processing data

The most basic technique to characterize batteries is CP (ChronoPotentiometry). It consists in applying a positive or negative constant current and recording the evolution of the cell voltage with time.

Nominal potential Charge

Discharge

CP

• Cycling under stepwise potentiodynamic mode.

• Potential sweep defined by setting the potential step amplitude and duration.

• Possible limit of the step duration on the charge or discharge currents value.

• Can be used for PITT (Potentiostatic Intermittent Titration Technique)

1 experiments.

Potentiodynamic Cycling with Galvanostatic Acceleration

1. C. John Wen et al. J. Electrochem. Soc. 126, 12, (1979) pp 2258-2266

PCGA

LiMn2O4-G_10Ah_PCGA_6-1q_01.mpr

Ew e vs. time <I> vs. time #

time/s

40 00035 00030 000

Ew

e/V

3,97

3,965

3,96

3,955

3,95

3,945

3,94

3,935

3,93

<I>

/mA

650

600

550

500

450

400

350

300

• Successive potential steps with a conditional limit on the minimum current

• Current measured as a function of time, which allows determination of the incremental capacity dx/dV more precisely than CP.

• No relaxation period.

• The magnitude of the current transient can be used to provide a measure of the chemical diffusion flux of the mobile species as a function of time t1.

• The main drawback is that the ohmic drop across the cell is not eliminated.

1. W. Weppner and R. A. Huggins, J. Electrochem. Soc. 126, 12, (1977) pp 2258-2266

PCGA

Galvanostatic Cycling with Potential Limitation

• Battery cycling under galvanostatic mode i.e. with an imposed current

• Possible voltage limitations under current for both charge (positive current) and discharge (negative current)

• GCPL can be used to perform GITT (Galvanostatic Intermittent Titration Technique)2 experiments.

• Similarly to PITT, GCPL can be used to have the chemical diffusion coefficient of the mobile species in the electrode.

GCPL

1. C. John Wen et al. J. Electrochem. Soc. 126, 12, (1979) pp 2258-2266

Charge sequence

Current control

Potential control once EM is reached

OCV period once the current limit Im is reached If Ewe is below EL after OCV, the

charge starts again.

GCPL

18650_GITT1.mpr

Ew e vs. time <I> vs. time #

time/s

60 00040 000

Ew

e/V

4,25

4,2

4,15

4,1

4,05

4

3,95<

I>/m

A

150

100

50

0

-50

-100

18650_GITT1_IQx.mpp

Ew e vs. x

x

0,80,60,4

Ew

e/V

4,2

4,1

4

3,9

3,8

3,7

3,6

3,5

It is now possible after processing to see the evolution of E vs x, which is the number of moles of inserted mobile species (Li+,OH-…).

GCPL

Processing

In case of a sluggish process, the charge/discharge is performed until EL is reached.

GCPL2 : GCPL with a limitation on the voltage of the working electrode and of the counter electrode.

GCPL3 : GCPL2 with the possibility to hold potential after charge or discharge.

GCPL4 : GCPL with the possibility to set the global time of the charge/discharge period.

GCPL5: GCPL with the possibility to calculate the dynamic resistance at different time .

GCPL6 : GCPL with a voltage control and limit on WE-CE.

GCPL7 : GCPL but the holding period is performed with a current control.

SGCPL : GCPL with a limitation on the external input/output

Other GCPL techniques

See Application Note #1, 2, 3 http://bio-logic.info/potentiostat/notesan.html

• Discharge of a battery at a constant resistance.

• Potentiostat seen as a constant resistor by the battery.

CLD: Constant Load Discharge CPW: Constant Power

• The current is controlled to hold E*I constant.

• Used for determination of Ragone plot (power vs. energy).

CLD/CPW

See Application Note #6, 33, 34 http://bio-logic.info/potentiostat/notesan.html

PPI

GPI

RPI

PWPI

Potentio: E control

Galvano: I control

Resistance: R control

Power: P control

• Up to 3000 sequences in the same technique

• Possibility to repeat one or several sequences

• Profile created step by step or imported from an ASCII file

Urban profile importation

GPI: European standard profile NEDCL on a 40 A.h LFP cell

• Green: discharge at a constant rate C/1

• Red: Temperature change during the constant discharge C/1

• Blue: discharge profile with 4 urban cycles and 1 extra urban cycle

• Repeated 6 times

• Red: Temperature change during the urban cycles

Urban profile importation

Outline

1. Configuration

2. DC techniques

3. Impedance spectroscopy

4. Processing data

Impedance Spectroscopy

• It can be performed either with an applied current (GEIS) or potential (PEIS) mode.

• It can be performed automatically at different states of charge by linking PEIS to GCPL.

• It is used to study the electrode-electrolyte interfaces.

• It can be used to evaluate the dependence of the impedance with the state of charge (SOC).

• It can be used to study aging of the battery (state of health = SOH).

See Application Note #5, 8, 9, 14, 15, 16, 17, 18, 19, 23 http://bio-logic.info/potentiostat/notesan.html See Impedance tutorial

Potentio EIS / Galvano EIS techniques

• EIS can performed with an increasing DC bias voltage and current.

• A patented drift correction can be applied to the battery if the steady state is not reached.

• There is a possibility to set sequences with different sinus amplitudes.

• A multisine mode can be used to reduce the measurement duration.

See Application Note #5, 8, 9, 14, 15, 16, 17, 18, 19, 23 http://bio-logic.info/potentiostat/notesan.html See Impedance tutorial

Impedance Spectroscopy

- Materials: Lithium Iron Phosphate LiFePO4 / Graphite - Nominal potential = 3,1V - Structure: 3D

After each discharge step, an EIS measurement can be performed at OCV. The corresponding EIS spectrum is changing, highlighting changing electrode/electrolyte interfaces.

Impedance Spectroscopy

C440_9-9d_PEIS_01.mpr

-Im(Z) vs. Re(Z)

Re (Z) /Ohm

0,0040,0030,0020,001

-Im

(Z

)/O

hm

0,001

0,0008

0,0006

0,0004

0,0002

0

-0,0002

-0,0004

-0,0006

-0,0008

-0,001

-0,0012

223 Hz

21 Hz

0,5 Hz

2.3 kHz

C394_9-9d_GEIS-5A.mpr

-Im(Z) vs. Re(Z)

Re (Z) /Ohm

0,0020,0015

-Im

(Z

)/O

hm

0,0004

0,0003

0,0002

0,0001

0

-0,0001

-0,0002

-0,0003

1Hz

485 Hz

47 Hz

Charged state Discharged state

Impedance Spectroscopy

The two impedance graphs can be fitted with an equivalent circuit using ZFit (see Impedance tutorial)

All the battery techniques are also available in stack mode.

• One master Z channel and up to 15 standard slave channels (= 30 cells) with VMP3.

• EIS or DC measurements on each element of the stack

• Possibility of linked experiments

Stacks

• Stack of 10 elements.

• The impedance of the stack is the sum of the impedance of each element.

• It allows to make a quick comparison of the different charging state of he batteries.

Stacks

Outline

1. Configuration

2. DC techniques

3. Impedance spectroscopy

4. Processing data

Two processing modes: standard and compact depending on the technique used.

Standard processing mode creates a new .mpp file with additional variables as chosen:

• Energy (charge/discharge)

• Intercalation coefficient x

• Qcharge / Qdischarge

• Cycle number, ....

• The number of data points will be the same as in the initial data file

Process Data

Compact processing mode calculates an averaged or integrated variable on every step (current or voltage depending the technique)

•Determination of the dynamic resistance with the GCPL5 technique

•Determination of the incremental capacity with a PCGA

Process Data

Processing to get capacity and energy per cycle

• Determination of energy, capacity and efficiency

• Separated for charge and discharge periods

• Stored in a .mpp file

Process Data

Other applications

All these techniques are also available for the study of other energy devices : • Fuel cells • Supercapacitors • Photovoltaic cells

Thank you for your

attention

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